Abstract: A driving mechanism comprises a rotatable shaft (34), a drive arm (56) mounted on and rotatable with said drive shaft and having a swing end projecting radially therefrom on which a counterbalanced drive link (63) is rotatably mounted and arranged to rotate in a plane parallel to the plane of rotation of the drive arm, means (65,66,67,68,69) for rotating said drive link in a direction which is opposite to that of said drive arm, balance means (71) forming a part of said drive arm and rotatable therewith about said drive shaft so as to counterbalance the weight of said drive arm (56) and drive link (63) irrespective of the angular position of said drive link (63) relative to said drive arm (56) and a pair of flexible cables (W1,W2), each interconnected at one end with a driven element (C) to be reciprocated and each being secured at its other end with a fixed element (51,54) and the intermediate portions of said links being looped about pulley means (50) mounted on the swing end of said drive link (63) in such